A device that utilizes a source synchronous interface provides a reference signal along with data sent from the device. The reference signal is generally referred to as a strobe signal or a data strobe (DQS) signal. One example of a source synchronous device (source) is a synchronous dynamic random access memory (SDRAM) device. The strobe signal sent from the source is used by the device (target) that is coupled to, and communicating with, the source.
The target device must synchronize with the strobe signal in order to capture data from the source and interpret the data correctly. Since sources can operate over a wide range of frequencies, a target must be able to synchronize with data strobe signals over a wide range of frequencies. Typically, the target utilizes a delay line to synchronize with the strobe signal. Strobe signals having lower frequencies have larger periods and, thus, require delay lines capable of providing a larger amount of delay to achieve synchronization as compared to higher frequencies. Delay lines, however, can consume a large portion of the area of an integrated circuit, particularly when used to synchronize with lower frequency strobe signals.
In some cases, the strobe signal accompanying the data provided by the source is inadequate for use by the target. For example, the strobe signal provided by the source generally stops providing pulses when the data stops. In some cases, the target is not finished propagating the received data to the desired destination within the target when the pulses on the strobe signal terminate.